Introduction of metal impurity to change workfunction of conductive electrodes

ABSTRACT

Semiconductor structures, such as, for example, field effect transistors (FETs) and/or metal-oxide-semiconductor capacitor (MOSCAPs), are provided in which the workfunction of a conductive electrode stack is changed by introducing metal impurities into a metal-containing material layer which, together with a conductive electrode, is present in the electrode stack. The choice of metal impurities depends on whether the electrode is to have an n-type workfunction or a p-type workfunction. The present invention also provides a method of fabricating such semiconductor structures. The introduction of metal impurities can be achieved by codeposition of a layer containing both a metal-containing material and workfunction altering metal impurities, forming a stack in which a layer of metal impurities is present between layers of a metal-containing material, or by forming a material layer including the metal impurities above and/or below a metal-containing material and then heating the structure so that the metal impurities are introduced into the metal-containing material.

FIELD OF THE INVENTION

The present invention relates to semiconductor structures, and moreparticularly to semiconductor structures such as, for example, fieldeffect transistors (FETs) or metal-oxide-semiconductor capacitors(MOSCAPs), in which the workfunction of a conductive electrode stack ischanged by introducing metal impurities into a metal-containing materiallayer which, together with a conductive electrode, is present in theelectrode stack. The choice of metal impurities depends on whether theelectrode is to have an n-type workfunction or a p-type workfunction.The present invention also provides a method of fabricating suchsemiconductor structures.

BACKGROUND OF THE INVENTION

In standard silicon complementary metal oxide semiconductor (CMOS)technology, n-type field effect transistors (nFETs) use an As or P (oranother donor) doped n-type polysilicon layer as a gate electrode thatis deposited on top of a silicon dioxide or silicon oxynitride gatedielectric layer. The gate voltage is applied through this polysiliconlayer to create an inversion channel in the p-type silicon underneaththe gate oxide layer.

In future technology, silicon dioxide or silicon oxynitride dielectricswill be replaced with a gate material that has a higher dielectricconstant. These materials are known as “high k” materials with the term“high k” denoting an insulating material whose dielectric constant isgreater than about 4.0, preferably greater than about 7.0. Thedielectric constants mentioned herein are relative to a vacuum unlessotherwise specified. Of the various possibilities, hafnium oxide,hafnium silicate, or hafnium silicon oxynitride may be the most suitablereplacement candidates for conventional gate dielectrics due to theirexcellent thermal stability at high temperatures.

Silicon metal oxide semiconductor field effect transistors (MOSFETs)fabricated with a hafnium-based dielectric as the gate dielectric sufferfrom a non-ideal threshold voltage when n-MOSFETs are fabricated. Thisis a general problem, and in particular, when the MOSFET consists ofHfO₂ as the dielectric and TiN/polySi as the gate stack, the thresholdvoltage is in the 0.45 to 0.7 V range typically after standard thermaltreatments. Ideally, the threshold voltage for long channel nFETs shouldbe around 0 to 0.2V or so.

In view of the above-mentioned problem with prior art Si MOSFETs thatinclude a Hf-based dielectric or other high k dielectric, there is aneed for providing a method and structure that is capable of stabilizingthe flatband voltages and threshold voltages in semiconductor structuresthat contain such high k gate dielectric materials.

SUMMARY OF THE INVENTION

The present invention provides semiconductor structures in which theworkfunction of a conductive electrode stack is changed by introducingat least one metal impurity to a metal-containing material layer that islocated between a conductive electrode and a high k dielectric. The term“high k dielectric” is used throughout the present application to denoteany insulating material whose dielectric constant is greater than thatof silicon dioxide. That is, the high k dielectrics employed in thepresent invention have a dielectric constant, as measured in a vacuum,that is greater than 4.0. The ability to change or modify theworkfunction of a material stack including a high k dielectric iscritical for improving the performance of a semiconductor device thatincludes the same.

It is noted that in the past, the workfunction of a material stackincluding a high k dielectric was changed by modifying the dielectric orby introducing a low or high workfunction metal under a gate stackincluding a metal layer and a gate electrode. In the present invention,the workfunction modification occurs by providing a gate stack thatincludes a metal impurity containing layer which is present beneath aconductive electrode.

In general terms, a semiconductor structure is provided that comprises:

a material stack comprising a dielectric having a dielectric constant ofgreater than silicon dioxide, a metal impurity containing layercomprising a metal-containing material and at least one workfunctionaltering metal impurity located above said dielectric, and a conductiveelectrode located above said metal impurity containing layer.

In a preferred embodiment of the present, a semiconductor structure isprovided that comprises:

a material stack comprising a Hf-based dielectric, a metal impuritycontaining layer comprising TiN or TiON and at least one workfunctionaltering metal impurity located above said Hf-based dielectric, and apolysilicon electrode located above said metal impurity containinglayer.

In addition to the semiconductor structures mentioned above, the presentinvention also provides a method of altering the workfunction of aconductive gate stack that includes:

providing a material stack that comprises a dielectric having adielectric constant of greater than silicon dioxide, a metal-containingmaterial layer located above said dielectric, and a conductive electrodelocated above said metal-containing material layer; and

introducing at least one workfunction altering metal impurity into saidmetal-containing material layer wherein said at least one workfunctionaltering metal impurity is introduced during forming of a metal impuritycontaining layer or after formation of a layer containing saidmetal-containing material layer.

In one embodiment of the present invention, the at least oneworkfunction altering metal impurity and said metal-containing materiallayer are formed by codeposition providing a metal impurity containinglayer containing both a metal-containing material and said at least onemetal impurity.

In another embodiment, a first layer of a metal-containing material isformed, followed by a layer containing the metal impurities, followed bya second layer of the metal-containing material.

In yet another embodiment of the present invention, a materialcontaining the metal impurities is formed below and/or above ametal-containing material and the metal impurities are then introducedinto the metal-containing material by a subsequent thermal process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E are pictorial representations (through cross sectionalviews) depicting basic processing steps, including alternativeembodiments, of the present invention.

FIGS. 2A-2B are semiconductor structures, a MOSCAP and a MOSFET,respectively that can include the inventive stack formed as illustratedin FIGS. 1A-1E.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a semiconductor structure in whichthe workfunction of a conductive electrode stack is changed byintroducing a metal impurity into a metal-containing material layer ofthe gate stack as well as a method of forming the same, will now bedescribed in greater detail by referring to the following discussion anddrawings that accompany the present application. It is noted that thedrawings of the present application are provided for illustrativepurposes and, as such, they are not drawn to scale. Also, like and/orcorresponding elements are referred to herein using like referencenumerals.

It is again emphasized that prior art Si MOSFETs fabricated with hafniumoxide as the gate dielectric suffer from a non-ideal threshold voltagewhen n-MOSFETs are fabricated. When the stacks consist of HfO₂ as thedielectric, and TiN/polysilicon as the gate stack, the long channel nFETthreshold voltage is in the range of 0.45 to 0.7 V range typically afterstandard thermal treatments. Ideally, the threshold voltage for longchannel nFETs should be around 0 to 0.2V or so. The present inventionsolves this problem by introducing at least one metal impurity into ametal-containing material layer of the gate stack that introduces ashift in the threshold voltage to the desired voltage.

The material stack of the present invention together with the processingsteps that are used in forming the same will be described first followedby a description of the same as a component of a MOSCAP and a MOSFET. Itis noted that although the MOSCAP and the MOSFET are shown as separatestructures, the present invention also contemplates structures whichinclude both the MOSCAP and the MOSFET on a surface of a singlesemiconductor substrate. It is also noted that in the present invention,the metal impurity containing layer and the conductive gate electrodeform a gate stack to which the inventive method is applicable.

Reference is first made to FIGS. 1A-1E which are pictorialrepresentations (through cross sectional views) depicting the basicprocessing steps that are used in forming the inventive material stackon the surface of a semiconductor substrate. FIG. 1A shows an initialstructure that is formed in the present invention that includes asemiconductor substrate 10, an optional interfacial layer 12 on asurface of the semiconductor substrate 10 and a high k, e.g., Hf-based,dielectric 14 that is located on the optional interfacial layer 12. Whenthe interfacial layer 12 is not present, the high k dielectric 14 islocated on a surface of the semiconductor substrate 10.

The semiconductor substrate 10 of the structure shown in FIG. 1Acomprises any semiconducting material including, but not limited to: Si,Ge, SiGe, SiC, SiGeC, GaAs, GaN, InAs, InP and all other III/V or II/VIcompound semiconductors. Semiconductor substrate 10 may also comprise anorganic semiconductor or a layered semiconductor such as Si/SiGe, asilicon-on-insulator (SOI), a SiGe-on-insulator (SGOI) or agermanium-on-insulator (GOI). In some embodiments of the presentinvention, it is preferred that the semiconductor substrate 10 becomposed of a Si-containing semiconductor material, i.e., asemiconductor material that includes silicon. The semiconductorsubstrate 10 may be doped, undoped or contain doped and undoped regionstherein. The semiconductor substrate 10 may include a single crystalorientation or it may include at least two coplanar surface regions thathave different crystal orientations (the latter substrate is referred toin the art as a hybrid substrate). When a hybrid substrate is employed,an nFET is typically formed on a (100) crystal surface, while a pFET istypically formed on a (110) crystal plane. The hybrid substrate can beformed by techniques such as described, for example, in U.S. Ser. No.10/250,241, filed Jun. 17, 2003, now U.S. Publication No. 20040256700A1,U.S. Ser. No. 10/725,850, now U.S. Publication No. 20050116290, filedDec. 2, 2003, and U.S. Ser. No. 10/696,634, filed Oct. 29, 2003, nowU.S. Publication No. 20050093104, the entire contents of each areincorporated herein by reference.

The semiconductor substrate 10 may also include a first doped (n- or p-)region, and a second doped (n- or p-) region. For clarity, the dopedregions are not specifically shown in the drawing of the presentapplication. The first doped region and the second doped region may bethe same, or they may have different conductivities and/or dopingconcentrations. These doped regions are known as “wells” and they areformed utilizing conventional ion implantation processes.

At least one isolation region (not shown) is then typically formed intothe semiconductor substrate 10. The isolation region may be a trenchisolation region or a field oxide isolation region. The trench isolationregion is formed utilizing a conventional trench isolation process wellknown to those skilled in the art. For example, lithography, etching andfilling of the trench with a trench dielectric may be used in formingthe trench isolation region. Optionally, a liner may be formed in thetrench prior to trench fill, a densification step may be performed afterthe trench fill and a planarization process may follow the trench fillas well. The field oxide may be formed utilizing a so-called localoxidation of silicon process. Note that the at least one isolationregion provides isolation between neighboring gate regions, typicallyrequired when the neighboring gates have opposite conductivities, i.e.,nFETs and pFETs. The neighboring gate regions can have the sameconductivity (i.e., both n- or p-type), or alternatively they can havedifferent conductivities (i.e., one n-type and the other p-type).

After processing the semiconductor substrate 10, an interfacial layer 12is optionally formed on the surface of the semiconductor substrate 10 bychemical oxidation. The optional interfacial layer 12 is formedutilizing a conventional wet chemical process technique that is wellknown to those skilled in the art. Alternatively, the layer may beformed by thermal oxidation or oxynitridation. When the substrate 10 isa Si-containing semiconductor, the interfacial layer 12 is comprised ofchemical oxide grown by wet processing, or thermally grown siliconoxide, silicon oxynitride or a nitrided silicon oxide. When thesubstrate 10 is other than a Si-containing semiconductor, theinterfacial layer may comprise a semiconducting oxide, a semiconductingoxynitride or a nitrided semiconducting oxide.

The thickness of the interfacial layer 12 is typically from about 0.5 toabout 1.2 nm, with a thickness from about 0.8 to about 1 nm being moretypical. The thickness, however, may be different after processing athigher temperatures, which are usually required during CMOS fabrication.

In accordance with an embodiment of the present invention, theinterfacial layer 12 is a silicon oxide layer having a thickness fromabout 0.6 to about 0.8 nm that is formed by wet chemical oxidation. Theprocess step for this wet chemical oxidation includes treating a cleanedsemiconductor surface (such as a HF-last semiconductor surface) with amixture of ammonium hydroxide, hydrogen peroxide and water (in a 1:1:5ratio) at 65° C. Alternately, the interfacial layer can also be formedby treating the HF-last semiconductor surface in ozonated aqueoussolutions, with the ozone concentration usually varying from, but notlimited to: 2 parts per million (ppm) to 40 ppm.

Next, a high k dielectric 14 can be formed on the surface of theinterfacial layer 12, if present, or the surface of the semiconductorsubstrate 10 by a deposition process such as, for example, chemicalvapor deposition (CVD), plasma-assisted CVD, physical vapor deposition(PVD), metalorganic chemical vapor deposition (MOCVD), atomic layerdeposition (ALD), evaporation, reactive sputtering, chemical solutiondeposition and other like deposition processes. The high k dielectric 14may also be formed utilizing any combination of the above processes.

The high k dielectric 14 employed in the present invention is anydielectric material having a dielectric constant of greater than about4.0, typically greater than about 7.0. Note that silicon dioxide has adielectric constant of 4.0 and, as such, the present inventioncontemplates any dielectric whose dielectric constant is greater thanthat of silicon dioxide. The high k dielectric 14 is typically a metaloxide or mixed metal oxide that is well known to those skilled in theart. Illustrative examples of such high k dielectrics include, but arenot limited: Al₂O₃, Ta₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃, ZrO₂, Y₂O₃,Gd₂O₃, Hf-based dielectrics (to be described in greater detail hereinbelow), and combinations including multilayers thereof. Preferably, thehigh k dielectric 14 is a Hf-based dielectric, which may optionalinclude a rare earth metal oxide as well.

The term ‘Hf-based dielectric’ is intended herein to include any high kdielectric containing hafnium, Hf. Examples of such Hf-based dielectricscomprise hafnium oxide (HfO₂), hafnium silicate (HfSiO_(x)), Hf siliconoxynitride (HfSiON) or multilayers thereof. In some embodiments, theHf-based dielectric comprises a mixture of HfO₂ and ZrO₂. Typically, theHf-based dielectric is hafnium oxide or hafnium silicate. Hf-baseddielectrics typically have a dielectric constant that is greater thanabout 10.0.

The physical thickness of the high k dielectric 14 may vary, buttypically, the high k dielectric 14 has a thickness from about 0.5 toabout 10 nm, with a thickness from about 0.5 to about 3 nm being moretypical.

In one embodiment of the present invention, the high k dielectric 14 ishafnium oxide that is formed by MOCVD were a flow rate of about 70 toabout 90 mgm of hafnium-tetrabutoxide (a Hf-precursor) and a flow rateof O₂ of about 250 to about 350 sccm are used. The deposition of Hfoxide occurs using a chamber pressure between 0.3 and 0.5 Torr and asubstrate temperature of between 400° and 500° C.

In another embodiment of the present invention, the high k dielectric 14is hafnium silicate which is formed by MOCVD using the followingconditions (i) a flow rate of the precursor Hf-tetrabutoxide of between70 and 90 mg/m, a flow rate of O₂ between 25 and 100 sccm, and a flowrate of SiH₄ of between 20 and 60 sccm; (ii) a chamber pressure between0.3 and 0.5 Torr, and (iii) a substrate temperature between 400° and500° C.

Next, and in one embodiment of the present invention, a metal impuritycontaining layer 18 comprising a metal-containing material and at leastone metal impurity is formed on the surface of the high k dielectric 14;See FIG. 1B. The metal impurity (i.e., peak concentration thereof) canbe continuously distributed throughout the entire thickness of layer 18or the metal impurity (peak concentration thereof) can be formed indiscrete regions within layer 18. For example, the metal impurities canbe present at or near the upper or lower surfaces of layer 18, withinapproximately the center of layer 18 or in any combination thereof.

The metal-containing material (layer 18 without the impurities)comprises a metallic material and/or a semimetallic material that iscapable of conducting electrons. Specifically, the metal-containingmaterial (layer 18 without the metal impurities) is a metallic materialsuch as a metal nitride, metal carbide or a metal silicon nitride. Inthe embodiment when the metal-containing material (layer 18 withoutmetal impurities) includes a metal, the metal component of themetal-containing material may comprise a metal from Group IVB or VB ofthe Periodic Table of Elements. Hence, the metal-containing material mayinclude Ti, Zr, Hf, V, Nb or Ta, with Ti being highly preferred. By wayof example, the metal-containing material preferably comprises TiN orTiON; note TiN is particularly useful in n-type devices, while TiON isparticularly useful in p-type devices.

The metal impurities which are used in the present invention to alterthe workfunction of the gate stack (e.g., combination of themetal-containing material (layer 18 without impurities) and theconductive electrode) are dependent upon whether the gate electrode willhave n-type wok function or p-type workfunction. Since the metalimpurities are used to alter the workfunction of the gate stack, theycan be referred to as “workfunction altering metal impurities”. Forn-type workfunctions, the metal impurities introduced into themetal-containing material comprise at least one element from GroupsIIIB, IVB or VB of the Periodic Table of Elements (the nomenclature ofthe elements is based on the CAS version). Elements within theLanthanide Series (e.g., La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er,Tm, Yb or Lu) also contemplated herein. Illustrative examples of metalimpurities that can be used in providing an n-type workfunction to aconductive electrode comprise, but are not limited to: Sc, Y, La, Zr,Hf, V, Nb, Ta, Ti and elements from the Lanthanide Series, with theproviso that the metal impurity is different from the metal present inthe ‘pure’ metal-containing material. Preferably, the impurity used inproviding the n-type workfunction shift is one element from theLanthanide group. For p-type workfunctions, the metal impuritiesintroduced into the metal-containing material comprise at least oneelement from Groups VIB, VIIB and VIII of the Periodic Table of Elements(the nomenclature of the elements is based on the CAS version).Illustrative examples of metal impurities that can be used in providinga p-type workfunction to a conductive electrode comprise, but are notlimited to: Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, and Pt, with the provisothat the metal impurity is different from the metal present in the‘pure’ metal-containing material. Preferably, the impurity used inproviding the p-type workfunction shift is one of Pd.

In this particularly embodiment of the present invention illustrated inFIG. 1B, the metal impurity containing layer 18 is formed utilizing acodeposition process in which both the metal-containing material (puremetal-containing material without impurities) and the impurities aredeposited at substantially the same time. The codeposition can beperformed by using a metallic or semimetallic target, e.g., Ti target,with a certain amount of impurity in the target and layer 18 can beformed within any reactor chamber. Another codeposition method that canbe used in the present invention in providing layer 18 is chemical vapordeposition or plasma enhanced chemical vapor deposition whereinprecursors of the metal-containing material and the impurity are used.

Notwithstanding the codeposition technique used, layer 18, whichincludes the desired impurity (or impurities), has an as depositedthickness from about 0.1 to about 0.2 nm, with a thickness from about0.1 to about 1 nm being even more typical.

In another embodiment of the present invention, a ‘pure’metal-containing material is first deposited, followed by a layer whichcontains the metal impurities, followed by another ‘pure’metal-containing material. The structure formed utilizing thisembodiment of the present invention is shown in FIG. 1C, for example. InFIG. 1C, reference numeral 18A denotes the first deposited ‘pure’metal-containing material, reference numeral 18B denotes a layer ofmetal impurities and reference numeral 18C denotes the second deposited‘pure” metal-containing material. It is noted that layers 18A, 18B, and18C form a metal impurity containing layer 18 that includes the ‘pure’metal-containing material and metal impurities.

In this embodiment of the present invention, the ‘pure’ metal-containingmaterial is formed utilizing a conventional deposition process such as,for example, CVD, PECVD, physical vapor deposition (PVD), atomic layerdeposition (ALD), sputtering or evaporation. In one embodiment of thepresent invention, the metal-containing material is TiN that isdeposited by evaporating Ti from an effusion cell held in the range of1550° to 1900° C., typically 1600° to 1750° C., and using anatomic/excited beam of nitrogen that is passed through a remote radiofrequency source. The substrate temperature can be around 300° C. andthe nitrogen flow rate can be between 0.5 sccm and 3.0 sccm. Theseranges are exemplary and by no way limit the present invention. Thenitrogen flow rate depends upon the specifics of the deposition chamber,in particularly, the pumping rate on the chamber. The TiN may bedeposited, in other ways, as well, such as chemical vapor deposition orsputtering and the technique is not critical.

The layer of metal impurity is formed also utilizing a conventionaldeposition process such as, for example, CVD, PECVD, PVD, ALD,sputtering or evaporation. The particular type of metal impurity withinlayer 18B includes the metal impurities listed above in the embodimentwherein codeposition was employed.

The thickness of the first deposited ‘pure’ metal-containing material18A may vary depending upon the type of material employed as well as thetechnique used in forming the same. Typically, the first deposited‘pure’ metal-containing material 18A has a thickness from about 0.1 toabout 0.2 nm, with a thickness from about 0.1 to about 1 nm being evenmore typical. The thickness of the second deposited ‘pure’metal-containing material 18C is typically within the ranges mentionedabove as well. The thickness of the layer 18B containing the metalimpurities may vary, but typically, layer 18B has a thickness from about0.1 to about 0.2 nm, with a thickness from about 0.1 to about 1 nm beingeven more typical.

In another embodiment of the present invention, a material (dielectric,sacrificial or conductive, for example) containing the metal impuritiesis formed above and/or below a ‘pure’ metal-containing material and thena thermal process is used to introduce the metal impurities to the‘pure’ electrically conductive material. This embodiment of the presentinvention is shown, for example, in FIG. 1D. In this drawing, referencenumeral 20 is used as defining the material that contains the metalimpurities and reference numeral 18A is used as defining the ‘pure’metal-containing material. In this embodiment of the present invention,at least one layer 20 of a material containing metal impurities needs tobe present and adjacent said ‘pure’ metal-containing material 18A. Thestructure shown is prior to the thermal process which introduces themetal impurities into layer 18A. In some embodiments, the material 20atop the structure may be removed after the impurities have beenintroduced into the ‘pure’ metal-containing material 18A.

The material containing the metal impurities 20 can be formed utilizingany conventional deposition process. Illustrative examples of depositionprocesses that can be used in forming layer 20 include, but are notlimited to: CVD, PECVD, ALD, evaporation, or chemical solutiondeposition. The thickness of layer 20 may vary depending on the materialof the layer as well as the technique used in forming the same.Typically, the material containing impurities 20 has a thickness fromabout 0.1 to about 2 nm, with a thickness from about 0.1 to about 0.2 nmbeing even more typical.

Layer 18A shown in FIG. 1D can be formed as described above and it maycomprise one of the above mentioned materials whose thickness is withinthe ranges as also described above.

As stated above, the metal impurities are introduced into layer 18Autilizing a thermal technique. The thermal technique typically followsthe formation of the structure shown in FIG. 1D. In some embodiments, alater thermal process can be used to introduce the metal impurities intolayer 18A. The thermal technique typically comprises a temperature thatis about 800° C. or greater, with a temperature from about 900° to about1200° C. being even more typical. The duration of this thermal techniquemay vary, with a range from about 1 to about 1000 seconds being typical.The thermal technique used for the introduction of the metal impuritiesinto layer 18A may comprise a furnace anneal, a source/drain activationanneal, a rapid thermal anneal, a spike anneal, a laser anneal, asubsequent deposition process in which the above mentioned temperaturerange is used, or any combination thereof.

Following the formation of one of the structures shown in FIGS. 1B, 1C,or 1D, a conductive electrode 22 is formed atop the upper most layer ofthe particular structure. The resultant structure including the gateelectrode 22 located atop the structure provided in FIG. 1B is shown inFIG. 1E. The other two structures (using the structure of FIGS. 1C and1D) would be similar to the one depicted in FIG. 1E and hence they arenot specifically shown herein.

Specifically, a blanket layer of a conductive material, which formed theconductive electrode 22, is formed on layer 18, or optionally layer 20,if the embodiment shown in FIG. 1D is used, utilizing a known depositionprocess such as, for example, physical vapor deposition, CVD orevaporation. The conductive material includes, but is not limited to:Si-containing materials such as Si or a SiGe alloy layer in eithersingle crystal, polycrystalline or amorphous form. The conductivematerial may also be a conductive metal or a conductive metal alloy.Combinations of the aforementioned conductive materials are alsocontemplated herein. Si-containing materials are preferred as theconductive electrode 22, with polySi being most preferred. In additionto aforementioned conductive materials, the present invention alsocontemplates instances wherein the conductive electrode 22 is fullysilicided or a stack including a combination of a silicide and Si orSiGe. The silicide is made using a conventional silicidation processwell known to those skilled in the art. Fully silicided gates can beformed using a conventional replacement gate process; the details ofwhich are not critical to the practice of the present invention. Theblanket layer of conductive electrode material may be doped or undoped.If doped, an in-situ doping deposition process may be employed informing the same. Alternatively, a doped gate conductor can be formed bydeposition, ion implantation and annealing. The ion implantation andannealing can occur prior to or after a subsequent etching step thatpatterns the material stack. Doping of the conductive electrode 22 willfurther shift the workfunction of the gate conductor formed.Illustrative examples of dopant ions for nMOSFETs include elements fromGroup VA of the Periodic Table of Elements (Group IIIA elements can beused when pMOSFETs are formed). The thickness, i.e., height, of theconductive electrode 22 deposited at this point of the present inventionmay vary depending on the deposition process employed. Typically, theconductive electrode 22 has a vertical thickness from about 20 to about180 nm, with a thickness from about 40 to about 150 nm being moretypical.

The material stack structure shown in FIG. 1E (optionally includinglayer 20 above and/or below layer 18) can then be fabricated into aMOSCAP 50 as shown in FIG. 2A or a MOSFET 52 as shown in FIG. 2Butilizing conventional processes that are well known in the art. Each ofthe illustrated structures includes a material stack such as shown inFIG. 1E which has been at least patterned by lithography and etching.

The MOSCAP formation includes forming a thermal sacrificial oxide (notshown) on the surface of the semiconductor substrate. Using lithography,the active areas of the capacitor structure are opened in the fieldoxide by etching. Following the removal of the oxide, the material stackas shown in FIG. 1E is formed as described above. Specifically, thematerial stack was provided, patterned by lithography and etching, andthen the dopants are introduced into the conductor 22. The dopants aretypically P (implant dose of 5E15 ions/cm² using an implant energy of 12keV). The dopants are activated using an activation anneal that isperformed at 950° C. to 1000° C. for about 5 seconds. In some cases, aforming gas anneal (5-10% hydrogen) can follow which is performedbetween 500° to 550° C. for interfacial layer/semiconductor substrateinterface state passivation.

The MOSFET formation includes first forming isolation regions, such astrench isolation regions, within the substrate as described above. Asacrificial oxide layer can be formed atop the substrate prior toformation of the isolation regions. Similar to the MOSCAP and afterremoving the sacrificial oxide, a material stack as described above isformed. Following patterning of the material stack, at least one spacer54 is typically, but not always, formed on exposed sidewalls of eachpatterned material stack. The at least one spacer 54 is comprised of aninsulator such as an oxide, nitride, oxynitride and/or any combinationthereof. The at least one spacer 54 is formed by deposition and etching.

The width of the at least one spacer 54 must be sufficiently wide suchthat the source and drain silicide contacts (to be subsequently formed)do not encroach underneath the edges of the patterned material stack.Typically, the source/drain silicide does not encroach underneath theedges of the patterned material stack when the at least one spacer 54has a width, as measured at the bottom, from about 20 to about 80 nm.

The patterned material stack can also be passivated at this point of thepresent invention by subjecting the same to a thermal oxidation,nitridation or oxynitridation process. The passivation step forms a thinlayer of passivating material about the material stack. This step may beused instead or in conjunction with the previous step of spacerformation. When used with the spacer formation step, spacer formationoccurs after the material stack passivation process.

Source/drain diffusion regions 56 are then formed into the substrate.The source/drain diffusion regions 56 are formed utilizing ionimplantation and an annealing step. The annealing step serves toactivate the dopants that were implanted by the previous implant step.The conditions for the ion implantation and annealing are well known tothose skilled in the art. The source/drain diffusion regions 56 may alsoinclude extension implant regions which are formed prior to source/drainimplantation using a conventional extension implant. The extensionimplant may be followed by an activation anneal, or alternatively thedopants implanted during the extension implant and the source/drainimplant can be activated using the same activation anneal cycle. Haloimplants are also contemplated herein.

In some cases, a forming gas anneal (5-10% hydrogen) can follow which isperformed between 500° to 550° C. for interfacial layer/semiconductorsubstrate interface state passivation.

The above processing steps form the structure shown in FIG. 2B. FurtherCMOS processing such as formation of silicided contacts (source/drainand gate) as well as formation of BEOL (back-end-of-the-line)interconnect levels with metal interconnects can be formed utilizingprocessing steps that are well known to those skilled in the art.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A semiconductor structure comprising: a material stack comprising adielectric having a dielectric constant of greater than silicon dioxide,a metal impurity containing layer comprising a metal-containing materialand at least one workfunction altering metal impurity therein locatedabove said dielectric, and a conductive electrode located above saidmetal impurity containing layer.
 2. The semiconductor structure of claim1 further comprising an interfacial layer located beneath saiddielectric.
 3. The semiconductor structure of claim 2 wherein saidinterfacial layer comprises a semiconducting oxide, a semiconductingoxynitride or a nitrided semiconducting oxide.
 4. The semiconductorstructure of claim 2 further comprising a semiconductor substratelocated beneath said interfacial layer.
 5. The semiconductor structureof claim 1 further comprising a semiconductor substrate located beneathsaid dielectric.
 6. The semiconductor structure of claim 1 wherein saiddielectric is a Hf-based dielectric comprising hafnium oxide, hafniumsilicate, hafnium silicon oxynitride, a mixture of hafnium oxide andzirconium oxide, or multilayers thereof.
 7. The semiconductor structureof claim 1 wherein said metal-containing material comprises a metalnitride, a metal carbide or a metal silicon nitride, wherein said metalis from Group IVB or VB of the Periodic Table of Elements.
 8. Thesemiconductor structure of claim 1 wherein said metal-containingmaterial comprises TiN or TiON.
 9. The semiconductor structure of claim1 wherein said at least one workfunction altering metal impurity is foraltering an n-type gate stack.
 10. The semiconductor structure of claim9 wherein said at least one workfunction altering metal impuritycomprises an element from Group IIIB of the Periodic Table of Elements,an element from Group IVB of the Periodic Table of Elements, an elementfrom Group VB of the Periodic Table of Elements or an element from theLanthanide Series.
 11. The semiconductor structure of claim 1 whereinsaid at least one workfunction altering metal impurity is for altering ap-type gate stack.
 12. The semiconductor structure of claim 11 whereinsaid at least one workfunction altering metal impurity comprises anelement from VIB of the Periodic Table of Elements, an element fromGroup VIIB of the Periodic Table of Elements or an element from GroupVIII of the Periodic Table of Elements.
 13. The semiconductor structureof claim 1 wherein said material stack is a component of a field effecttransistor, a metal oxide semiconductor capacitor or a combinationthereof.
 14. A semiconductor structure comprising: a material stackcomprising a Hf-based dielectric, a metal impurity containing layercomprising TiN or TiON and at least one workfunction altering metalimpurity located above said Hf-based dielectric, and a polysiliconelectrode located above said metal impurity containing layer.
 15. Thesemiconductor structure of claim 14 further comprising an interfaciallayer located beneath said dielectric.
 16. The semiconductor structureof claim 15 wherein said interfacial layer comprises a semiconductingoxide, a semiconducting nitride or a semiconducting oxynitride.
 17. Thesemiconductor structure of claim 15 further comprising a semiconductorsubstrate located beneath said interfacial layer.
 18. The semiconductorstructure of claim 14 further comprising a semiconductor substratelocated beneath said dielectric.
 19. The semiconductor structure ofclaim 14 wherein said dielectric Hf-based dielectric comprises hafniumoxide, hafnium silicate, hafnium silicon oxynitride, a mixture ofhafnium oxide and zirconium oxide, or multilayers thereof.
 20. Thesemiconductor structure of claim 14 wherein said metal impuritycontaining layer comprises TiN.
 21. The semiconductor structure of claim14 wherein said metal impurity containing layer comprises TiON.
 22. Thesemiconductor structure of claim 14 wherein said at least oneworkfunction altering metal impurity is for altering an n-type gatestack.
 23. The semiconductor structure of claim 22 wherein said at leastone workfunction altering metal impurity comprises an element from GroupIIIB of the Periodic Table of Elements, an element from Group IVB of thePeriodic Table of Elements, an element from Group VB of the PeriodicTable of Elements or an element from the Lanthanide Series.
 24. Thesemiconductor structure of claim 14 wherein said at least oneworkfunction altering metal impurity is for altering a p-type gatestack.
 25. The semiconductor structure of claim 24 wherein said at leastone workfunction altering metal impurity comprises an element from VIBof the Periodic Table of Elements, an element from Group VIIB of thePeriodic Table of Elements or an element from Group VIII of the PeriodicTable of Elements.
 26. The semiconductor structure of claim 14 whereinsaid material stack is a component of a field effect transistor, a metaloxide semiconductor capacitor or a combination thereof.
 27. A method ofchanging workfunction of a conductive stack comprising: providing amaterial stack that comprises a dielectric having a dielectric constantof greater than silicon dioxide, a metal-containing material locatedabove said dielectric, and a conductive electrode located above saidmetal-containing material; and introducing at least one workfunctionaltering metal impurity into said metal-containing material wherein saidat least one workfunction altering metal impurity is introduced duringforming of a metal impurity containing layer or after formation of alayer containing said metal-containing material.
 28. The method of claim27 wherein said introducing the at least one workfunction altering metalimpurity into said metal-containing material comprises codeposition ofthe at least one workfunction altering metal impurity and themetal-containing material.
 29. The method of claim 28 wherein saidcodeposition comprises sputtering or chemical vapor deposition.
 30. Themethod of claim 27 wherein said introducing the at least oneworkfunction altering metal impurity into said metal-containing materialcomprises forming a first layer of the metal-containing material,forming a layer containing the metal impurities on said first layer, andforming a second layer of the metal-containing material.
 31. The methodof claim 27 wherein said introducing the at least one workfunctionaltering metal impurity into said metal-containing material comprisesforming a material layer containing the metal impurities below and/orabove the metal-containing material, and subjecting the material stackto a thermal process.